1. Field of the Invention
This invention relates generally to projectiles, and in particular, to training projectiles having components for inducing in-flight aerodynamic effects on the projectile.
2. Description of the Prior Art
Use of shape memory alloys (SMA) is shown in U.S. Pat. No. 4,941,627. This technology discloses a control fin having a shape memory effect alloy to change the angle of attack of the rear stabilizer fins of a guided projectile in response to an electrical current. That disclosure includes control, and further discloses fins that impart aerodynamic or hydrodynamic lift to alter the path of the vehicle as opposed to imparting a rapid in-flight increase in aerodynamic drag to slow the vehicle down. Other limitations of this fin design include a need for a external power supply to provide an electrical current that is required to actuate the control fins. This limitation alone incurs greater increase in weight, volume and cost requirements to build the projectile.
Another training projectile is in U.S. Pat. No. 5,874,691 entitled xe2x80x9cKinetic Energy Collapsible Training Projectile,xe2x80x9d which is hereby incorporated by reference. This disclosure includes training projectiles comprising in combination, a nose; a body having a forewardmost end and a rearwardmost end, wherein the forewardmost end is secured to the nose; and a tail including fins secured to the rearwardmost end of the body. This is shown in FIG. 1 The body may or may not contain buttress grooves. These grooves provide an attachment surface for sabots. Sabots provide an integral metallic or composite plastic section which mates the projectile and with the gun tube or cannon tube. The sabot provides a surface for the gun gasses to act upon during the gas propulsion phase of the firing event. The gas pressure is thereby converted to mechanical energy in the form of projectile acceleration down the cannon tube.
Kinetic energy training projectiles differ from tactical projectiles in that they are not designed for target penetration. They are used for target practice. Thus, there is a need for types of training projectile rounds (munitions) that have similar physical appearance and handling characteristics (to the tactical cartridges they represent). These training projectiles have limited maximum range (for safety purposes at a training range), but can be designed to traverse several thousand meters from a firing device to a desired target.
To date there is a need in the munitions art to provide a cost effective and accurate training round that uses xe2x80x9cpassivexe2x80x9d control mediums to limit the flight trajectory of such a round. The present invention addresses this problem.
The present invention uses aerodynamic heating caused by air-friction during flight of a training projectile. The training projectile includes a nose, a body and a tail section. The body has a forwardmost end secured to the nose, and a rearwardmost end secured to the tail. Air friction during flight causes deployment of xe2x80x9cpassivexe2x80x9d shape memory alloy (SMA) aerodynamic members in an assembly to induce drag of the training projectile thereby limiting an effective range of the projectile. The word xe2x80x9cpassivexe2x80x9d herein means that no ancillary electrical supply or other type of heat creating power supply is required to actuate the SMA material in this assembly, thus minimizing or eliminating added weight, volume and cost requirements of a projectile as discussed above. The types of shape memory alloy materials that can be used in the assemblies herein exhibit martensitic phase transformations. The SMA materials include elements selected from the group consisting of Nickel, Silver, Gold, Cadmium, Indium, Gallium, Thallium, Silicon, Germanium, Tin, Antimony, Zinc, Niobium, Copper, Iron, Platinum, Aluminum, Manganese, and Titanium, to provide actuation of each of the embodiments of the training projectile. Four embodiments of the present invention are discussed below.
The first embodiment includes use of SMA materials formed in strip members externally attached to the nose assembly of the projectile. These strip members deploy in-flight to induce aerodynamic drag. These strips are elongated and initially remain flat and maintain a smooth contour of the nose section prior to deployment in-flight. When deployed, these strips are designed with a spoiler-type contour dependent on required kinetic energy characteristics of the projectile and desired range of the test projectile. Variations of this embodiment include incorporating these strips either along the mid-body section or the tail section of the projectile. Various combinations of these three sections of the projectile can incorporate these strips.
The second embodiment of the invention includes a SMA material spring element within a nose assembly that causes deployment of sliders and drag inducing aerodynamic elements outwards from the nose section when in flight. This nose assembly includes the SMA spring element, a sliding lock member in cooperation with the SMA spring element, a nose tip and another spring and slider element.
The third embodiment of the invention includes a SMA ring member as part of a segmented nose assembly. This assembly includes at least a bifurcated composite body of the nose assembly that splits apart when the SMA ring member contracts (shrinks) during flight and allowing each nose segment member to splay from the root section attached to the body mid-section portion of the training projectile. The nose assembly can be made of other forms such as a three, four or more parts having substantially equal volume sections of the nose assembly.
The fourth embodiment of the invention includes a SMA materials incorporated in either the nose, body, or fin section alone or combinations of these sections. For example, the body section will be that is attached to a nose section (which can be ogival, conic, and hemispherical, in shape) and to a tail section (which can be a fin or spin stabilization device) and can incorporate a SMA in any one of these sections. This SMA body section will change shape when stimulus from aerodynamic heating occurs during flight. In this way, both the center of pressure and the center of gravity of the projectile will be affected, causing flight instability of the projectile. One possible example of this embodiment could be designed such that the body wraps around itself in a knot like fashion, while the nose section and tail section remain attached (or discarded).
One advantage of the present invention is to provide a training projectile that simulates the trajectory of an actual tactical projectile (using passive SMA components) up to and including through where the target is positioned. Upon passing through the target, the training projectile using the present invention, changes trajectory so that the projectile will fall to the ground within a predetermined distance along a predetermined path (trajectory) beyond the target (such as a maximum range requirement).
Another advantage of the present invention is to provide a training projectile that can be produced by standard machining techniques.
A further advantage of the present invention is to provide a kinetic energy training projectile that maintains predetermined aerodynamic design characteristics of actual tactical projectiles during flight.
Yet another advantage of the invention is that training round production costs can be saved by using xe2x80x9cpassivexe2x80x9d SMA deployable members. Extensive costs can be saved as a result of using SMA in in place of expensive servo motors, explosive devices, micromechanical devices, or external power sources.
Still further advantages will become apparent by reference to the following description and the accompanying drawings.